According to Newton's third law of motion, for every action, there is an equal and opposite reaction. In practical application in an industrial machine, when a motor is activated to move a mass or object, the object exerts a reaction force on the motor equal to the force generated to the object by the motor. This reaction force acts on the motor as well as on parts connected to the motor. As a result, the reaction force received by the motor, if sufficiently large, causes vibration or shock to the machine.
Vibration and shock are undesirable and will affect machine performance, especially in the semiconductor industry where speed and precision are important. An example is when creating wire bonds to make electrical connections between electrical contacts on a semiconductor die and a leadframe using a wire bonder machine. A motor has to move an object, namely a bond head and attached ultrasonic transducer of the machine, between different predetermined electrical contacts on the die and the leadframe. To achieve higher throughput, the motor has to move the bond head at a high speed. However, reaction forces created by the driving movement acts on the motor and motor platform, causing vibration of the same. Thus, precision may be sacrificed at the expense of speed if such vibration is not attenuated. Conversely, to achieve higher precision, the bond head has to be driven at a lower speed.
A conventional solution is to separate a body of a driving motor from its platform or base. A vibration insulator is inserted between the motor body and its base. In this way, vibration forces from the motor body to the rest of the machine can be dampened by the vibration insulator. However, since the body of the motor is no longer rigidly fixed, there is a need for more critical control requirements and complicated control algorithms.
There have also been attempts in other industries to attempt to cancel vibrational forces. An example of this is described in U.S. Pat. No. 5,231,336 for “Actuator for Active Vibration Control”. An electromagnetic actuator is arranged so that a moving element undergoes reciprocal motion in response to an electrical input signal. The moving element is decoupled from any mechanical load in one embodiment so as to produce reaction forces which may be used to cancel vibrational forces. However, a drawback of the device described therein is that it requires a vibration sensor to sense the vibrations of a vibrating surface before the vibrations are processed by a processing unit to produce a suitable feedback. The processing unit generates a driving signal to electromagnetic coils to impart motion to an armature in such a manner as to produce reaction forces to reduce the sensed vibrations. This means that vibrations need to be sensed first, then measured, before a counteracting force is generated to reduce the vibrations. This solution is not sufficiently responsive where vibration forces are continually changing, and there is not sufficient time to sense an amount of vibration before seeking to counteract such vibration.
In the light of the above disadvantages, it would be desirable to develop a solution wherein the effects of vibrational forces are reduced in an efficient and substantially instantaneous manner while having a motor's main body fixed to the rest of the machine for stability.